1. Field of the Invention
The present invention relates generally to power systems, and more specifically, to a system and method of regulating charging current to batteries in a battery power-plant.
2. Background Art
Users have become increasingly reliant upon electronic systems to perform critical functions. Some electronic systems must be operational at all times. For instance, telecommunication systems, such as switching systems and cellular stations, must handle thousands of calls per second. The failure of such systems due to power loss, is unacceptable since it would result in the loss of millions of telephone calls and the severe disruption of commerce.
Critical electronic systems typically rely on battery plants to maintain a high level of constant operational availability. Battery plants employ backup batteries to provide power when a commercial (or non-commercial) power supply is off-line or unavailable; especially in rural areas. It is therefore, necessary to keep batteries charged prior to a power outage or recharge batteries following a power unavailability to avoid depleting battery reserves.
In many applications, such as cellular, it is necessary to charge batteries as rapidly as possible to regain battery storage reserves in advance of further power source unavailability. To charge batteries in shorter periods of time, it is necessary to raise their voltage to a higher level, which can result in excessive current flowing to the batteries. Excessive charging current can physically damage batteries reducing their effective life or destroy them. Additionally, excessive charging currents cause batteries to "out gas" giving off quantities of toxic gasses, which present severe health, environment and safety concerns.
To prevent excess charge currents most sophisticated power supplies have some type of static current limit control to provide protection from excessive current during abnormal conditions, such as a short circuit in the connected equipment (load). Such a static current limit control is typically set manually to a desired level and left unchanged. During normal conditions the load draws less current than the current limit setting of the power supply and the supply functions as constant voltage source. During abnormal conditions when the load requires more current than the current limit setting, the current limit becomes active restricting the current to the load (i.e., the power supply functions as a constant current source). In the latter case, when the load requires more energy, it is possible to starve the batteries, since current from the power supply is limited.
Additionally, if a power plant with static current limit control is modified, for instance, to include more batteries, it is necessary to manually change the current limit setting. Such modifications may require hardware changes as well as possible design changes to the system, which is costly and restrictive.
Further, it is sometimes desirous to remove the load during low voltage conditions. However, static current limit sensors are designed to assume that a load current is always present. Accordingly, when the load current is removed, it is possible to allow excessive current to reach the batteries and possibly damage or destroy them, since the current flowing from the power source is assumed to include a load component, which is absent in this scenario.
Thus, what is a needed is an improved power plant design with a less restrictive current control schemes, able to dynamically account for variations in load current while protecting the batteries from excess charging current.